Photosensitive material for radiography

ABSTRACT

A RADIOGRAPHIC ELEMENT CAPABLE OF BEING HANDLED UNDER YELLOW SAFELIGHTS, THE ELEMENT CONTAINING A FILTER DYE WHICH ITSELF IMPORTS TO THE ELEMENT A DENSITY TO YELLOW LIGHT OF NOT LESS THAN 0.4 AND A DENSITY TO BLUE LIGHT OF NOT GREATER THAN 0.1.

PHOTOSENSITIVE MATERIAL FOR RADIOGRAPHY Filed April 26, 1971 W/ll/fl mamJ m H Mm m T 0 W m5 m C m 4 V w/ 1 B 1 United States Patent 3,705,807PHOTOSENSITIVE MATERIAL FOR RADIOGRAPHY Vinicio Busatto, Savona, Italy,assignor to Minnesota Mining and Manufacturing Company Filed Apr. 26,1971, Ser. No. 137,179 Claims priority, application Italy, Apr. 24,1970, 50,263/ 70 Int. Cl. G03c 1/84 US. Cl. 96-84 R 8 Claims ABSTRACT OFTHE DISCLOSURE A radiographic element capable of being handled underyellow safelights, the element containing a filter dye which itselfimparts to the element a density to yellow light of not less than 0.4and a density to blue light of not greater than 0.1.

The present invention relates to a photosensitive material forradiographic use.

Radiographic materials which are employed for industrial and for medicaluses are often similar. In general, the photosensitive material forindustrial radiography is employed to photograph internal parts ofmetallic bodies; the photosensitive material for medical radiography isgenerally employed to photograph internal parts of animal bodies,especially the human body.

Frequently the same radiographic material may be used both forindustrial as well as for medical radiography. In both cases, X-rayspass through the object to be radiographed and expose, either directlyor indirectly, radiographic material. Two reinforcing shields may beemployed, one of them placed between the X-ray source and theradiographic film, the other one placed behind the film itself.

Radiographic material, as is known, commonly employs a transparentsupport (e.g., cellulose triacetate or of polyester), which has anemulsion layer coated on each side and which has protecting layerscoated on the emulsion layers, the construction thus having at leastfive layers including the transparent support layer.

The radiographic, material support generally displays a silght bluecoloration, the yellow density (i.e., the density measured with yellowlight) which is due to the blue coloration of the film being of theorder of 0.13 (Westrex Densitometer filter Status A).

The photosensitive emulsions for radiography are usually based on silverbromo-iodide which have maximum sensitivity to blue-violet radiationsand minor sensitivity to the X-rays. Such emulsions show somesensitivity to the blue-green radiations and exhibit low sensitivity tohigher wave length radiations (e.g., green or red).

The protective layers are generally of gelatin and of gelatin hardenerssuch as aldehydes, salt of chromium and aluminum, and mucochloric acid.The protective layers serve to protect the emulsion layers fromscratches, etc.

The reinforcing shields such as those referred to above (sometimesreferred to as intensifier screens) may be metallic (e.g., lead,tantalum) and saline, the latter referring to a sheet of paper or ofplastic material bearing on a face a paste consisting of a dispersion ingelatin, or, in another similar medium, of a product such as leadsulfate, barium sulfate, calcium tungstate, zinc sulfide, the leadstruck by X-rays emits slow neutrons which are easily absorbed by theemulsion giving rise for the formation of a latent image. Saline shieldsemit a blue-violet light for which the photosensitive emulsion forradiography has maximum sensitivity. Lead is used as a shield in thecase of radiographic films for industrial use, whereas saline shieldsare generally used in the case of radiographic films for medical usebecause less X-ray exposure is required. Saline shields, however, can beemployed in industrial radiography as well.

The fact that photosensitive emulsions for radiography exhibit highsensitivity to blue-violet light, some sensitivity to blue-green lightand low sensitivity to higher wave length radiations (e.g., green,green-yellow, yellow, orange and red), permits safety lights havingwavelengths of from green to red to be used during manufacture andprocessing of radiographic materials. However, such safety lights mustbe of low intensity to avoid undue exposure of the radiographic materialwhich may lead to fogging. Particularly useful are those safety lampshaving emission maxima at wavelengths of from 580 to 620 m Sodium lamps,for example, have an emission maximum in the range of 580600 m Workingat the necessarily low light intensities, however, results inconsiderable inconvenience for the operator.

The object of the present inveniton is to provide a radiographicmaterial which can be handled under safety lights of high intensity forrelatively long periods of time without risk of undue exposure.

Briefly, the present invention relates to a radiographic element whichincludes a base layer, a silver halide photographic emulsion layercarried on each surface of the base layer, and a protective layercarried by each emulsion layer. The element contains filter dye which ishighly absorptive of yellow light (e.g., light at 580- 620 mg) and ishighly transmissive of blue light (e.g., light at 410-450 mg). The dyeis present in an amount sufiicient to itself impart to the element adensity to yellow light of not less than 0.4 and a density to blue lightof not more than 0.1. In the preferred embodiment, the dye isdistributed in layers of the element such that (a) the base layerprovides 15-35% of said density to yellow light, and

(b) the emulsion layers together provide not less than one-half of saiddensity to yellow light which is not not provided by the base layer.

In the most preferred embodiment, the dye is distributed through each ofthe base, emulsion, and protective layers, the base layer providing15-35% of said density to yellow light and the emulsion layers togetherproviding at least half of the density to yellow light not provided bythe base layer. Preferably, the dye is distributed symmetrically in theelement with respect to the base layer.

In particular the filter layers should display an absorption curve witha density minimum in the zone ranging from 360 to 500 m nt, and amaximum in the zone ranging from 580 to 700 m l. The minimum of theabsorption curve should substantially correspond to the wave length atwhich the reinforcing shields are emitting (if reinforcing shields areemployed) and the maximum of the absorption curve should substantiallycorrespond to the maximum of the emission curve of the safety lampemployed. Since safety lamps which are especially useful are the sodiumlamps, which have an emission maximum ranging between 580 and 600 mg (azone in which the eye is particularly sensitive), filter layers having amaximum of absorption in the same zone are desired; on the other handsince the most commonly used shields are those ones containing e.g.,calcium tungstate (which emits in the zone of 410-450 mg) filter layershaving a minimum of absorption in this zone are desired. In generalfilter layers useful to the present invention objedtives are layerscontaining a blue filter dye.

Each of the layers composing the radiographic material can betransformed into a filter layer by introduction thereto of a dye havingthe desirable absorption characteristics.

It has now been found, for example, that in order to easily handle aradiographic material, Without fogging it under a safety light of 2.5lux (emanated from a sodium lamp filtered through a yellow filter), theradiographic material should have an absorption in the yellow such asthat shown in FIG. 1. Suflicient dye is employed in the element so as toitself provide a density to yellow light of not less than 0.4 (toprevent fogging by yellow safelights) and a density to blue light of notmore than 0.1 so as to maintain blue light sensitivity of the element.It has further been found that the capacity of a radiographic element towithstand exposure to yellow light and yet retain good blue lightsensitivity is also sensitive to the placement of the dye in layers ofthe element. Thus it has been found that optimum results are obtainedwhen the supporting layer contains dye in an amount sufficient toprovide from -35% of the total density of the element to yellow lightimparted by dye, and when the emulsion layers together contain dye inand amount suificient to enable these layers to provide at least half ofthat density to yellow light which is not provided by the supportinglayer. Preferably, as noted above, the dye is included within each layerof the element.

The dye in the emulsion and protective layers may be chosen so as to bedecolorable in photographic processing baths. If this dye is notdecolorable in processing baths, the finished radiograph has a pleasantbluish aspect, and it can be observed for a long time on a negatoscopewithout causing eye fatigue. On the other hand, if this dye isdecolorable in photographic processing baths, then the finishedradiograph will be of a lighter bluish hue for viewing. The dye of thesupporting layer, of course, is not decolorable.

Blue dyes which are decolorable in photographic processing baths includefor instance, the blue dyes described in the US. Pat. No. 3,260,601, andthe dyes corresponding to the following structural formulas:

II N Dyes which are not decolorable in the processing baths and whichare useful to the objectives of the present in- 4 vention include theeuprophthalocyanine (CI 74160) corresponding to the formula:

(5) Methylene Blue (CI 52015) (zinc double chloride) and (6) (CI 52030),(zinc double chloride) Cuprophthalocyanine dyes are preferred. Theinvention may be better understood by reference to the followingillustrative, non-limiting examples:

EXAMPLE 1 2200 g. of a high sensitivity radiographic emulsion containing5% of gelatin and 1.4 moles of silver halide (98.2% bromide and 1.8%iodide) was prepared.

Thereafter 1820 g. of a coating solution for providing protective layerswas prepared:

G. Deionized water 1453.0

Gelatin 71.4 10 g. of silica dispersion in 1000 cc. of a 10% gelatinsolution 286.0 Potassium nitrate (aqueous 25% solution) 3.7 "Manoxol N(Hardware and Holden Ltd., sodium dinonylsulfonsuccinate) 2.5 10%mucochloric acid solution in toluated methyl alcohol 3.4 Correction topH 6 The silver halide emulsion was coated on each face of a transparentblue polyester support having a density equivalent to 0.16 as read onthe Westrex Densitometer filter Status A, to provide a silver coverageequivalent to 4.5 g./m. Then over each emulsion layer was coated aprotective layer having a thickness of 1.35 The thusprepared isdesignated material 0 as a reference material.

A No. 1 material was prepared in the same manner as the referencematerial, except that the 1820 g. of protec tive solution contained 6.84g. of cuprophthalocyanine added in the form of a 2% aqueous suspension,equivalent to 0.125 g./m. of individual protective layer.

The No. 2 material, according to the present invention, was prepared inthe same manner as the reference material except that the 2200 g. ofemulsion contained 4.32 g. of cuprophthalocyanine added in the form of a2% aqueous dispersion equivalent to 0.125 g./m. of emulsion layer.

The No. 3 material, according to the present invention, was prepared inthe same manner as the reference material, except that the 1820 g. ofprotective solution contained 4.08 g. of cuprophthalocyanine added inthe form of a 2% aqueous dispersion equivalent to 0.075 g./m. ofprotective layer, and that the 2200 g. of emulsion contained 1.75 g. ofcuprophthalocyanine added in the form of a 2% aqueous solution,equivalent to 0.050 g./m. of emulsion layers.

No. 4 material was prepared in the same manner as the referencematerial, but using a colorless transparent polyester support instead ofa colored support and containing in the 1820 g. of protective solution,9.54 g. of cuprophthalocyanine added in the form of a 2% aqueoussolution equivalent to 0.173 g./m. of protective layer in the finishedproduct.

No. material was prepared in the same manner as the reference materialexcept that a transparent colorless support instead of a colored supportwas used. The 2200 g.

and in a Ferrania F 11 fixing bath having the following composition:

G. Sodium hyposulfite crystals 400 Anhydrous sodium bisulfite 30 Fusedsodium acetate 20 Boric acid crystals Potassium alum Water to 1000 cc.

The fog data are indicated in Table No. 2.

The data of the column headed 0 indicate the densities of the unexposed,processed samples. The numbers not in parentheses in the other columnsindicate the density of the exposed and processed samples. The data inparentheses indicate the density increase due to exposure of the varioussamples to yellow light. The density values were measured with aQuantalog Densitometer, TD-102, white light.

of emulsion contained 6.05 g. of cuprophthalocyanine TABLE 2 EXAMPLE 2added in the form of a 2% aqueous solution equivalent to 0.173 g./m. ofemulsion layer in the finished product.

No. 6 material was prepared in the same manner as the reference materialexcept that a transparent colorless support was usedinstead of a coloredsupport. The 1820 g. of protective solution contained 5.72 g. ofcuprophthalocyanine added in the form of a 2% aqueous solutionequivalent to 0.103 g./m. of protective layer in the finished product,and the 2200 g. of emulsion contained 2.44 g. of cuprophthalocyanineadded in the form of a 2% aqueous solution equivalent to 0.070 g./m. ofemulsion layer in the finished product.

Table 1 indicates the values of the density to yellow light which isimparted to each of certain layer of the above constructions by theincorporation therein of dye. Measurements were made with a WestrexDensitometer, filter Status A.

TABLE 1 Metol 3 Anhydrous sodium sulfite 5O Hydroquinone 9 Anhydroussodium carbonate (Soda Solway) 50 Potassium bromide 3 Water to 1000 cc.

A reference material A analogous to the reference material of Example 1but less sensitive to light was prepared. Then a material B was preparedin the same manner except that to the 1820 g. of protective solution wasadded 2.72 g. of cuprophthalocyanine (equivalent to 0.050 g./m. ofprotective layer) and to the 2200 g. of emulsion was added 2.64 g. ofcuprophthalocyanine (equivalent to 0.070 g./m. of emulsion layer in thefinished product). The two materials were exposed and processed, asdescribed Example 1, and the fog was similarly measured. The resultingdata appears in Table 3 as follows:

[O 0 seven? What is claimed is:

1. A radiographic element which includes a base layer, a silver halidephotographic emulsion layer carried on each surface of the base layer,and a protective layer carried by each emulsion layer, said elementcontaining filter dye which is highly absorptive of yellow light andhighly transmissive of blue light, and which is present in an amountsufiicient to itself impart to said element a density to yellow light ofnot less than 0.4 and a density to 'blue light of not greater than 0.1.

2. The element of claim 1 wherein said dye is distributed in layers ofsaid element such that the base layer provides from 15% to 35;% of saiddensity to yellow light and said emulsion layers together provide notless than one half of said density to yellow light which is not providedby said base layer.

3. The element of claim 1 wherein said dye is a cuprophthalocyanine dye.

4. The element of claim 2 wherein said dye is included in each of saidbase, emulsion, and protective layers.

5. The element of claim 2 wherein the dye in said emulsion andprotective layers is decolorized in photographic processing solutions.

6. A radiographic element which includes a base layer, a silver halidephotographic emulsion layer carried on each surface of the base layer,and a protective layer carried by each emulsion layer, said elementcontaining filter dye which is highly absorptive of yellow light andhighly transmissive of blue light and which is present in an amountsufiicient to itself impart to said element a density to yellow light ofnot less than 0.4 and a density to blue light of not greater than 0.1,the dye in said base layer being non-decolora'ble in photographicprocessing baths and the dye in other layers of said element beingdecolorable in photographic processing baths.

7. The radiographic element of claim 6 in which each emulsion layercontains a blue filter dye which is decolorable in photographicprocessing baths and each protective layer containing a blue filter dyewhich is decolorable in photographic processing baths.

References Cited UNITED STATES PATENTS 2,112,217 3/1938 B aldsiefen 9684R 2,489,662 11/1949 Murray 96-84 R 3,237,008 2/1966 Dostes 9684 R3,260,601 7/1966 Bailey 96-84 R RONALD H. SMITH, Primary Examiner U.S.Cl. X.R. 9682

